Republican presidential front-runner Donald Trump, at a Fox News-hosted town hall in Indianapolis, on Wednesday blasted rival Ted Cruz’s decision to announce a running mate even though he’s losing the nomination race – calling it a “waste of time.”

The back-and-forth capped an unusual day on the campaign trail, even as the nomination seems within Trump's grasp. The billionaire businessman responded to Cruz’s campaign curveball, while also elaborating on a foreign policy speech he delivered earlier in the day, at the forum hosted by Greta Van Susteren.

“I think it’s really a waste of time, honestly,” Trump said of Cruz’s decision to name former presidential candidate and ex-HP CEO Fiorina as his VP pick. Of the race, Trump said, “It should be over.”

Cruz earlier acknowledged it was “unusual” to name a VP choice so early, but defended the decision. He claimed “nobody is getting to 1,237 delegates,” the number needed to clinch the nomination, and voters should “know what [they] will get.”

After Trump swept five states across the Northeast on Tuesday, the three remaining GOP candidates are looking next to Indiana’s primary on May 3 as a pivotal point in the race – one that can show whether Trump turns his winning streak into irreversible momentum, or whether Cruz and John Kasich still have a shot at preventing him from clinching the nomination before July.

But Trump cast Cruz’s ticket roll-out Wednesday as a bid to distract from bad headlines, calling it “awfully early” for such an announcement.

“You have to first get the nomination. … He has zero chance,” he said.

Trump declined to go into detail about his own potential running mate choices. “I have a lot of great people. I just don’t like to talk about it right now,” he said.

In an interview Wednesday night on "The Kelly File" with Fox News' Megyn Kelly, Fiorina responded to Trump's comments over Cruz making her his VP pick.

"Donald Trump hasn't won this nomination yet, despite so many people in the media just wishing it would all be over," she said.

"This isn't over until someone reaches 1,237 (delegates) ... and no, close doesn't count," she added.

Fiorina told Kelly that parts of the Republican Party are uniting behind Cruz, with him receiving endorsements from former presidential candidates Gov. Scott Walker, Jeb Bush, in addition to Sen. Lindsey Graham of South Carolina.

“A majority of Republican voters don’t want Donald Trump to be their nominee," Fiorina said Wednesday.

She also responded to a question by Kelly over her criticism of Cruz earlier in the presidential campaign.

"In the heat of a presidential campaign, like in a basketball game, you make some fouls," she said.

Trump spoke just hours after delivering what was billed as a major foreign policy address in Washington. In the speech, Trump called for a drastic shake-up in America’s foreign policy – including “getting out of the nation-building business” and demanding NATO allies pay their “fair share” or be left to “defend themselves.”

At the Fox News town hall, Trump questioned “at what point are we the guardian of the world,” saying countries have to protect themselves “or you have to pay us properly.”

“We have to be good to our allies, but they have to remember that we’re good, and they have to take care of us,” Trump said.

He also discussed his goals for bringing jobs back to America, and – when asked about Bernie Sanders’ plans for free college tuition – said he would like to look “seriously” at bringing down college costs. He said he would, if elected, work out a “deal” to address that, potentially to include giving students more time to pay back their debt.

Trump was joined onstage Wednesday by legendary Indiana University basketball coach Bobby Knight, now a Trump supporter, who called the candidate “far and away the best person to lead America back to where we all want to be.”

Trump sought to demonstrate his foreign policy chops Wednesday as he tries to present a more presidential image – while increasingly turning his attention on the campaign trail to a general election battle he presumes will involve him and Hillary Clinton.

The billionaire businessman declared himself the “presumptive nominee” Tuesday night, after winning primaries in Connecticut, Delaware, Rhode Island, Pennsylvania and Maryland. He hasn’t shelved the trash talk and provocative language on the campaign trail, not yet anyway – repeatedly accusing Clinton of playing the “woman card” and mocking remaining GOP rivals Cruz and Kasich.